The present invention relates to the separation of a selected gas from a mixture of gases by pressure swing adsorption. The primary goal is to maximize the ratio of selected gas volume to energy input while minimizing the ratio of mechanical volume of the separator to the selected gas volume. The present invention separates, from the gas mixture, a concentration of one or more components of a gas mixture for delivery or storage.
Pressure swing adsorption (PSA) is a frequently used method to separate one component of a gas mixture. For example, pressure swing adsorption is used to separate concentrated oxygen from air and then deliver it to a patient for medical purposes. A common use in home medical care is the delivery of 90-95% concentrated oxygen, derived from the atmosphere, at rates up to 6 liters per minute for the treatment of emphysema or other diseases of the lungs in the home. The machines used for this purpose are large, bulky, heavy, and require a large amount of power to operate, thus making battery power impractical. Patients must have a supply of bottled oxygen available when they leave their home because use of an oxygen concentrator outside the home is not convenient or practical. Use of bottled oxygen is undesirable because of its disadvantages: limited operating capacity, heavy weight and hazardousness.
PSA is widely used in industrial gas separation processes as well. Industrial PSA processes vary in the type of gas mixture used and selected gas separated.
Generally PSA involves injecting a mixture of gas into a gas separation chamber having an adsorbent bed or molecular sieve bed. One gas is readily adsorbed when pressurized above atmospheric pressure in the adsorbent bed, while the other gas is less adsorbed. Both of the separated gases may be utilized or one may preferentially be used while the other is vented as waste. The adsorbed gas in the adsorbent bed is released upon lowering the gas separation chamber to the original atmospheric pressure, at such time purging the adsorbent bed. In order to achieve sufficient concentration of the separated gas, two or more adsorbent beds are used in either sequential or multi-processing modes. It is common to purge the bed of the adsorbed gas by using a portion of the product gas in order to improve the efficiency of the process.
The selected gas in the mixture can be either adsorbed with the remaining mixture, vented to atmosphere, or otherwise removed. Alternatively, the undesirable components may be adsorbed leaving the selected gas to be passed on for storage or immediate use. The adsorbed component is then discharged as a waste gas, stored or utilized immediately dependant upon the application.
To further clarify, the following is a description of a typical continuous process.
(1) Feed gas mixture (A+B) into a container with an adsorbent bed, at some pressure above atmosphere until the bed is saturated.
(2) Gas B must be adsorbed and stopped before it exits the product end. Gas A is moved to temporary or permanent storage from the product end.
(3) Reduce pressure on adsorbent bed.
(4) Extract gas B from the feed end while taking a fraction of gas A and feeding it back into the product end to purge gas B.
(5) Stop feeding gas A into the product end before it exits from the feed end.
(6) Return to step 1.
An example of this process is disclosed in U.S. Pat. No. 5,415,683 entitled xe2x80x9cVACUUM PRESSURE SWING ADSORPTION PROCESSxe2x80x9d.
Methods of providing portability, as disclosed in U.S. Pat. No. 4,971,609 entitled xe2x80x9cPORTABLE OXYGEN CONCENTRATORxe2x80x9d and U.S. Pat. No. 4,826,510 entitled xe2x80x9cPORTABLE LOW PROFILE DC OXYGEN CONCENTRATORxe2x80x9d, attempt to reduce the physical packaging design and provide on-demand flow, thereby improving efficiency and portability. These designs are severely limited because they do not improve the inherent low efficiency of the PSA process. The prior art requires an amount of energy impractical for sustained battery operation, a small compact size and lightweight apparatus, while still producing the necessary flow rate and product gas concentration. Inefficiencies arise in the PSA process from the following sources: (a) resistance to gas flow through the adsorbent bed, (b) energy losses in the pressurization/depressurization process, (c) irreversible thermal losses, and (d) inefficiencies in compressors, gas pumps and valves. Negating these inefficiencies while maintaining the desired flow rate and concentration is required in order to achieve a smaller, lightweight overall machine package capable of battery operation.
The present invention is a gas separator device using pressure swing adsorption to separate from a gas mixture the concentration of one or more components of that mixture.
The present invention is a gas separator for separating a gas mixture into a product gas. The gas separator has an adsorbent bed including a separation chamber with first and second ports and a molecular sieve material contained in the separation chamber. A first pumping chamber is connected to the first port. A first valve regulates a flow of the gas mixture between the first port and the first pumping chamber. A first piston is located in the first pumping chamber. A second pumping chamber is connected to the second port. A second valve regulates a flow of the product gas between the second port and the second pumping chamber. A second piston is located in the second pumping chamber. A drive system coordinates operation of the first and second pistons and the first and second valves in a cycle including a pressurization stage, a gas shift stage, and a depressurization stage.